1. Field of the Invention
The present invention relates to a display panel, and more particularly, to an organic electroluminescence display panel and a method for fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for decreasing line resistance and improving adhesion between a glass substrate and a seal-cover, thereby enhancing efficiency and durability of the organic electroluminescence display panel.
2. Discussion of the Related Art
Recently, a wide range of self-emissive luminescent display devices has been developed. However, the basic structure of such devices includes using a luminescence device that operates a single pixel as the main element, whereby the luminescence device is in planar alignment. Plasma display panels (PDP) using cells divided by discharge areas as a luminescence device, vacuum fluorescence displays (VFD), electroluminescence displays (ELD), light-emitting diodes (LED), and field emission displays (FED) can be given as examples of the above-described display devices.
Among such display devices, the organic electroluminescence (EL) display panel using an organic electroluminescence device as its main element, which provides a high-luminance surface emission at a low voltage and also an RGB light emission having a high color purity depending upon the selected material. Accordingly, the organic electroluminescence display panel is viewed as one of the most prominent display devices having the characteristics of slim design, lightweight, and full color representation.
The organic electroluminescence device is formed of an organic layer including an emission layer between a pair of electrodes formed of an anode having a positive voltage applied thereto and a cathode having a negative voltage applied thereto. By applying a voltage between the electrodes, an electron is injected into the organic layer from the cathode, and a hole is injected into the organic layer from the anode. Subsequently, the electron and the hole are paired to each other within the organic layer, thereby emitting light.
The organic electroluminescence display panel formed of the organic electroluminescence device having the above-described structure will now be described with reference to the accompanying drawings.
FIG. 1 illustrates a plane view of a general organic electroluminescence display panel.
Referring to FIG. 1, an indium-tin-oxide (ITO) strip 102 is linearly aligned in a strip form on a glass substrate 101. Subsequently, a counter electrode 103 having a width narrower than the ITO strip 102 is formed on the ITO strip 102. And, an organic electroluminous (EL) layer 104 formed of a hole transport layer, an emission layer, and an electron transport layer serially deposited thereon, is formed over the ITO strip 102. An insulating layer 106 is formed between the ITO strip 102 and a barrier rib. A cathode strip 105 formed in the shape of a strip overlaps the ITO strip 102 above the organic EL layer 104. Then, a barrier rib 107 formed in the shape of a strip is formed between each cathode strip 105, so as to separate the cathode strips 105 adjacent to one another. Finally, the organic EL display panel is completed when the substrate having the cathode strips 105 formed thereon is paired with a seal-cover 109 by using a sealant 108.
Herein, the organic EL display panel is formed of the organic EL layer 104 inserted between the ITO strip 102 having a high work function and the cathode strip 105 having a low function on the glass substrate 101. The ITO strip 102 having a high work function is used as an anode for injecting a hole, and the cathode strip 105 having a low work function is used as a cathode for injecting an electron.
FIGS. 2A to 2F illustrate perspective views of the process steps for fabricating the general organic electroluminescence display panel.
Referring to FIG. 2A, the ITO strip 102 (i.e., a transparent electrode) for applying an anode is formed on the glass substrate 101. Simultaneously, an ITO strip 102-A having a shorter length is formed between the barrier rib 107, so as to facilitate the removal of the cathode strip 105 in a later process.
Subsequently, as shown in FIG. 2B, the counter electrode 103 is formed of a highly conductive metal, such as molybdenum (Mo) and chrome (Cr). Herein, at a vertical crossing point between the sealant 108 used in the sealing process and the counter electrode 103, when the width of the counter electrode 103 is larger than the width of the ITO strip 102, the sealant 108 formed on the counter electrode 103 cannot be hardened during a hardening process of the sealant 108 by using UV light rays in a later process step. Therefore, at the crossing point between the sealant 108 and the counter electrode 103, the width of the counter electrode 103 is formed to be smaller than that of the ITO strip 102 formed thereunder.
Thereafter, referring to FIGS. 2C and 2D, in order to insulate the cathode strip 105 from the ITO strip 102, the insulating layer 106 and the barrier rib 107 are formed on the ITO strip 102. Herein, the insulating layer 106 is formed of an organic compound, an inorganic compound, a polymer, and a blended form of the same.
Furthermore, as shown in FIGS. 2E and 2F, the organic EL layer 104 is deposited over the insulating layer 106 and the barrier rib 107, so as to form the cathode strip 105, which is formed of a magnesium (Mg)-silver (Ag) alloy and aluminum (Al) or other conductive materials.
In the organic EL display panel having the above-described structure, the role of the sealing process is very important to the durability and efficiency of the display panel, which will now be described in detailed with reference to FIGS. 3A and 3B.
FIG. 3A illustrates a cross-sectional view of the panel taken along an X direction of FIG. 2F. And, FIG. 3B illustrates a cross-sectional view of the panel taken along a Y direction of FIG. 2F.
The organic EL display panel completed by the fabrication process shown in FIGS. 2A to 2F have the following problems. More specifically, referring to FIGS. 3A and 3B, when hardening the sealant 108 with UV light rays in a later process, if the width of the counter electrode 103 is larger than that of the ITO strip 102 at the point where the sealant 108 and the counter electrode 103 vertically cross each other, then the UV light rays cannot be transmitted through the counter electrode 103, which is formed of a metal. Therefore, an unhardened sealant 108-A remains on the counter electrode 103, as shown in FIG. 3B.
As described above, if the sealant 108 at the crossing point between the sealant 108 and the counter electrode 103 is not hardened, then the glass substrate 101 and the seal-cover 109 cannot be adhered to each other, which results in a penetration of moisture and oxygen, thereby causing a critical influence on the durability of the organic EL display panel.
Meanwhile, in order to resolve such problems and to facilitate the hardening of the sealant 108, a portion of the counter electrode 103 formed on the area where the sealant 108 is sprayed can either be removed or be dividedly formed in thin layers, as shown in FIG. 4.
However, when the portion of the counter electrode 103 formed on the area where the sealant 108 is sprayed is either removed or dividedly formed in thin layers, a line resistance is increased, thereby causing the problem of an increase in the driving voltage. Since the organic EL display panel is driven by electric current, the driving voltage increases as the line resistance rises.
Furthermore, since a plurality of cathode strips 105 is connected to a single ITO strip 102, a large amount of electric current is flown therein, thereby causing the efficiency of the organic EL display panel to be highly sensitive to the resistance.